1. Field of the Invention
This invention relates to a method of and an apparatus for a telephone system for radiotelephone communications, and more particularly to an improved telephone system for radiotelephone communications utilizing pulse-code-modulation (PCM) techniques.
2. Description of the Prior Art
Prior art telephone systems for radiotelephone communications have included a single base station for covering a large service area, for example, an entire city, which is in turn connected to a telephone central office. The base station typically had a plurality of duplexed radio channels for providing radiotelephone service to a somewhat limited number of mobile radiotelephones in a densely populated city. Expansion of service to a large number of radiotelephones could only be accomplished by adding more radio channels to such radiotelephone systems. However, the number of radio channels for use in such radiotelephone systems is limited both by governmental regulation and the unavailability of other radio channels. As a result, more mobile radiotelephones had to be added to the existing system, thereby creating congestion on the system's limited number of radio channels.
The problems of the foregoing prior art telephone systems have been solved to some degree by improved radiotelephone systems utilizing a plurality of base stations located in geographical cells. The base stations are operated at relatively low power such that the radio channels assigned to a first base station can be reused by a second base station that is sufficiently distant from the first base station to prevent radio frequency interference. By reusing the available radio channels throughout a large geographical area, a greater number of mobile radiotelephones can be accommodated by such radiotelephone systems.
However, in order to control the operation of such radiotelephone systems, a more complex switching network is required that can handle a large number of remotely located base stations and a large number of mobile radiotelephones including both vehicular and hand-held or portable radiotelephones. In addition, it is highly desirable that the switching network is designed to be capable of providing to the mobile radiotelephones all the telephone service features which are presently available to land-line telephones. For example, these telephone service features include services such as repertory dialing, automatic call forwarding, and automatic conference calling. None of the prior art radiotelephone systems is capable of providing any of these features. Thus, prior art radiotelephone systems cannot accommodate a relatively large number of mobile radiotelephones nor provide the foregoing and similar automatic telephone service features to mobile radiotelephones.
For the foregoing and other shortcomings and problems, there exists a need for an improved telephone system for radiotelephone communications that is capable of handling a large number of base stations and mobile radiotelephones and capable of providing many different standard and unique service features to the mobile radiotelephones.